Articles with dispersed conductive coatings

ABSTRACT

A conductive article includes a substrate made of a thermoplastic resin, and a transparent and conductive layer comprising carbon nanotubes and formed on at least one face of the substrate. The carbon nanotubes are electrical in contact with each other and dispersed so that each of the carbon nanotubes is separated form other carbon nanotubes, or that each of bundles of the carbon nanotubes is separated from other bundles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an articles that have a conductive layer andoptionally a light transmittance, and to methods for producing sucharticles.

2. Description of the Background

An anti-electrostatic resin plate that is able to release staticelectricity and avoid dust adherence has been used for a clean roompartition such as windows used in the clean room. One such example isdescribed in Japanese Laid Open Patent Publication 2001-62952. The resinmaterial of this invention includes tangled fibers that would extend atthe time of article formation to provide a good conductivity. Asubstrate film, where ITO (Indium Tin Oxide) or ATO (Antimony Tin Oxide)is placed on the surface, has been known as a transparent conductivefilm with a surface resistivity of 10⁰ to 10⁵Ω/□(Japanese Laid OpenPaten Publication 2003-151358).

In the conventional anti-electrostatic transparent resin plate (JapaneseLaid Open Paten Publication 2001-62952), the carbon fibers bent andintertwined with each other are buried in an anti-electrostatic layer.Therefore, the carbon fibers are not well dispersed. The amount of thecarbon fiber in the anti-electrostatic layer should be increased to acertain level in order to achieve an adequate surface resistivity of 10⁵to 10⁸Ω/□. The anti-electrostatic transparent resin plate (Japanese LaidOpen Paten Publication 2001-62952) mentioned can acquire anelectromagnetic shield property when the amount of the carbon fiber inthe anti-electrostatic layer is further increased and the surfaceresistivity decreases to 10⁴Ω/□. However, the transparency of theanti-electrostatic layer is deteriorated when the amount of the carbonfiber is increased. Thus, it is difficult to acquire the practicalanti-electrostatic transparent resin plate that has both goodtransparency and electromagnetic shield property.

The transparent conductive film described in the Japanese Laid OpenPaten Publication 2003-1 51358 is formed through a batch method such asspattering. Therefore, it has a poor productivity and the highproduction cost.

SUMMARY OF INVENTION

The present invention overcomes the problems and disadvantagesassociated with current strategies and designs and provides articleswith conductive layers that demonstrate good conductivity, whileacquiring better transparency, and to methods for forming such articles.

One embodiment of the invention is directed to articles with conductivelayers that can achieve good conductivity, with the same amount or lessof the ultra fine conductive fiber such as conventionally availablecarbon fiber.

Another embodiment of the invention is directed to methods for formingarticles with the conductive layers that demonstrate a goodconductivity, the thickness of which is reduced to improve thetransparency, which may be by reducing the amount of the ultra fineconductive fiber.

Another embodiment of the invention is directed to method for formingarticles with the transparent conductive layer that can be produced withlow production costs.

Other embodiments and advantages of the invention are set forth in partin the description, which follows, and in part, may be obvious from thisdescription, or may be learned from the practice of the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of the conductivearticle of this invention.

FIG. 2A is a cross-sectional view showing the dispersion of the ultrafine conductive fiber in the conductive layer of this invention, andFIG. 2B is another cross-sectional view showing the dispersion of theultra fine conductive fiber in the conductive layer of this invention.

FIG. 3 is a plan diagram of the conductive layer showing the dispersionof the ultra fine conductive fiber in the conductive layer.

FIG. 4 is a transmission electron microscopic photograph showing thedispersion of the ultra fine conductive fiber in the conductive layerviewing from above.

FIG. 5 is a scanning electron microscopic photograph showing thedispersion of the ultra fine conductive fibers in the conductive layerviewing from above.

FIG. 6 is an optical microscopic photograph showing the ultra fineconductive fiber in the conductive layer of the comparative exampleviewing from above.

DESCRIPTION OF THE INVENTION

As embodied and broadly described herein, the present invention isdirected to articles that have conductive coatings, which may optionallybe transparent, and methods of forming such articles.

One embodiment of the invention is directed to conductive articles thathave transparent conductive layers comprising ultra fine conductivefibers on at least one surface of a substrate. A characteristic of thisinvention is that the ultra fine conductive fibers are well dispersed,and yet in contact with each other, without densely concentrated.

The conductive article of this invention has a transparent conductivelayer that has the ultra fine conductive fiber on at least one surfaceof the substrate. Another characteristic of this invention is that theultra fine conductive fibers are in contact with each other and yetdispersed so that each fiber is separated from other fibers or eachbundle of the fiber, where a plurality of the fibers make a bundle, isseparated from other bundles.

The carbon fiber, especially carbon nanotube is used as the ultra fineconductive fiber in this invention. It is preferable that the fibers orthe bundles of the fiber are in contact with each other and yetdispersed so that each fiber or bundle is separated from other fibers orbundles. It is also preferable that the surface resistivity of thearticle be 10⁰ to 10¹¹Ω/□. Also, the surface resistivity of theconductive layer is 10⁰ to 10¹Ω/□ and the light transmission of thelight with 550 nm wavelength is above 50%. The surface resistivity ofthe conductive layer is 10² to 10³Ω/□ and the light transmission of thelight with 550 nm wavelength is above 75%. Or the surface resistivity ofthe conductive layer is 10⁴ to 10⁶Ω/□ and the light transmission of thelight with 550 nm wavelength is above 88%, or the surface resistivity ofthe conductive layer is 10⁷ to 10¹¹Ω/□ and the light transmission of thelight with 550 nm wavelength is above 93%.

The conductive article of this invention has a transparent conductivelayer made of thermo-plastic resin that has the carbon nanotube on atleast one surface of the substrate made of a transparent thermo-plasticresin. Another characteristic of this invention is that the carbonnanotubes are in contact, yet dispersed so that each tube is separatedfrom other tubes, and not densely concentrated.

The expression ‘not densely concentrated’ herein denotes that there isno significant lump of fibers with the average diameter of above 0.5 μmwhen the conductive layer is observed by an optical microscopy. The word‘contact’ indicates the following two states; the carbon nanotubes makean actual contact with each other, or the carbon nanotubes are locatedclose enough with a slight space between them that allows the flow ofelectricity. The word ‘conductivity’ means that the surface resistivityfalls into the scope of 10⁰ to 10¹¹Ω/□ when it is measured by JIS K 7194(ASTM D 991) (when the resistivity is below 10⁶Ω/□) or JIS K 6911 (ASTMD 257) (when the resistivity is above 10⁶Ω/□).

The ultra fine conductive fibers in the conductive layer of the firstconductive article of this invention are in contact with each other, andyet well dispersed without being densely concentrated. The ultra fineconductive fibers are loosely crossing each other, which allows for theflow of electricity, leading to the excellent conductivity. Therefore,the same conductivity as that of the conventional art can be obtainedwith the smaller amount of the ultra fine conductive fiber, allowing theimproved transparency and the thinner conductive layer. Since the fibersare not densely concentrated, the number of the fibers contributing tothe flow of electricity increases when the same amount of the ultra fineconductive fiber as that of the conventional art is applied, leading tothe improved conductivity. Furthermore, if the carbon nanotube, which isthin and long, is used as the ultra fine conductive fiber, the contactbetween the fibers is further facilitated, allowing the control of thesurface resistivity with the scope of 10⁰ to 10¹¹Ω/□. It is alsopossible to obtain a good transparency. The article of this inventioncan also have the anti-electrostatic property, the conductive property,and the electromagnetic shield property.

The ultra fine conductive fibers or bundles of the fiber in anotherconductive article of this invention are in contact with each other, yetdispersed so that each fiber is separated from other fibers or each ofthe bundle of fiber, where a plurality of the fibers make a bundle, isseparated from other bundles. The frequency of fibers or bundles offibers that make contact with each other increases, which allows for theflow of electricity, leading to excellent conductivity. Therefore, thesame conductivity as that of the conventional art can be obtained withthe smaller amount of the ultra fine conductive fiber, allowing for theimproved transparency and a thinner conductive layer. The improvedconductivity is obtained when the same amount of the ultra fineconductive fiber as that of the conventional art is applied, because thefrequency for the fibers to make contact with each other has beenincreased. Furthermore, if carbon nanotubes are used as ultra fineconductive fibers, contact between the fibers is further facilitated. Itis also possible to obtain the article with a good transparency and thearticle with the improved conductivity. The article of this inventioncan also have the anti-electrostatic property and the electromagneticshield property.

Various preferred embodiments of the invention may be explained byreferring to figures. However, this invention is not limited to thoseembodiments.

FIG. 1 is a cross-sectional view of the conductive article in the plateform of an embodiment of this invention. FIG. 2A is a cross-sectionalview showing the dispersion of the ultra fine conductive fiber in theconductive layer. FIG. 2B is another cross-sectional view showing thedispersion of the ultra fine conductive fiber in the conductive layer.FIG. 3 is a plan diagram showing the dispersion of the ultra fineconductive fiber in the conductive layer.

A conductive article P has a conductive layer 2 with ultra fineconductive fibers laminated on one (upper) surface of a substrate 1 thatis made of inorganic material such as synthetic resin, glass orceramics. The conductive layer 2 can be formed both upper and bottomsurfaces of the substrate 1.

The substrate 1 is made of thermo-plastic resin, the hardening resinthat is hardened by the application of heat, ultra-violet ray, electricbeam or radioactive ray, glass, ceramics, or inorganic material. Thetransparent thermo-plastic resin, hardening resin, or glass is adesirable material for acquiring the transparent conductive article P.The transparent thermo-plastic resin includes, for example, olefin resinsuch as polyethylene, polypropylene, and ring polyolefin, vinyl resinsuch as polyvinylchloride, polymethylmethacrylate, and polystyrene,cellulose resin such as nitrocellulose and triacetylcellulose, esterresin such as polycarbonate, polyethyleneterephtalate,polydimethylcyclohexeneterephtalate, and aromaticpolyester, ABS resin,the co-polymer and the mixture of these resins. The transparenthardening resin includes epoxy resin, polyimid resin and acrylic resin.The substrate 1 does not necessarily take the plate form, but maycomprise other forms as well.

The transparent resin with the light transmission of above 75%,preferably above 80%, and the haze of below 5% when the thickness of thesubstrate 1 is 3 mm, is especially desirable. Such resin includes ringpolyolefin, polyvinylchloride, polymethylmethacrylate, polystyrene,triacetylcellulose, polycarbonate, polyethyleneterephtalate,polydimethylcyclohexeneterephtalate, co-polymer of these resins, mixtureof these resins and hardening acrylic resin. Since glass has theexcellent light transmission of above 95%, glass is used frequently foracquiring the transparent conductive article P.

The ease of forming, the thermo-stability and the durability againstweathering of the substrate 1 made of resin mentioned above are improvedwhen an adequate amount of plasticizer, stabilizer and ultra-violet rayabsorbent are added. The substrate 1 can also be made opaque orsemi-opaque by adding die or pigment. In this case, an opaque or asemi-opaque conductive article is acquired. Since the conductive layer 2is transparent, the color of the die or pigment can be kept intact. Thethickness of the substrate 1 should be determined according to theusage, but the thickness of the substrate is usually about 0.03 to 10mm.

The conductive layer 2 formed on one side of the substrate 1 is atransparent layer that has the ultra fine conductive fiber 3. The ultrafine conductive fibers 3 are in contact with each other, and yetdispersed without being densely concentrated. That is, the fibers orbundles of the fiber, where a plurality of the fibers makes a bundle,are in contact with each other and yet dispersed so that each fiber isseparated from other fibers or each bundle is separated from otherbundles. The fibers will be in one of the following three states whenthe conductive layer 2 is formed with the ultra fine conductive fiber 3and a binder; the ultra fine conductive fibers are dispersed asdescribed above in the binder, as shown in FIG. 2A; the ultra fineconductive fibers are dispersed as described above, with a part of thefiber is in the binder and other part of the fiber protrudes or exposesitself from the binder, as shown in FIG. 2B; or the combination of thetwo. That is, the ultra fine conductive fibers are dispersed asdescribed above, where some fibers are buried in the binder as shown inFIG. 2A and a part of other fibers protrudes or exposes itself from thebinder as shown in FIG. 2B.

The dispersion of the ultra fine conductive fiber 3 viewing from aboveis shown in FIG. 3. The ultra fine conductive fibers 3 or bundles of thefiber are in contact with each other and yet dispersed so that eachfiber or each bundle is separated from other fibers or other bundles.The fibers are not intensely intertwined so that they are not denselyconcentrated. The fibers are simply crossing each other, making contactwith each other in or on the conductive layer 2. Since the fibers areloosely crossing, spreading in a broader area compared to the case wherethe fibers are densely concentrated, the frequency for the ultra fineconductive fiber to make contact with each other is greater, achievingthe excellent conductivity. The same frequency of the fiber contact (thedensity of the flow of electricity) should be acquired to achieve thesame conductivity of 10⁵ to 10⁸Ω/□ as that of the conventional art.Since the fibers are dispersed as described above, the smaller amount ofthe ultra fine conductive fiber allows the same frequency of the fibercontact, leading the better transparency. It is also possible to makethe conductive layer thinner, achieving the even better transparency.

It is not necessary for the ultra fine conductive fibers 3 or bundles ofthe fiber to be completely separated from other fibers or bundles. Smalllumps of fibers with diameters of less than 0.5 μm is acceptable.

The frequency of the fiber contact is higher in this invention than thatof the conventional art when the same amount of the ultra fineconductive fiber 3 is applied to the conductive layer 2, leading to theimproved conductivity.

Additionally, the conductivity can be improved even if the thickness ofthe conductive layer 2, which has the ultra fine conductive fiber 3, isreduced to 5 to 500 nm. Therefore, it is desirable to reduce thethickness of the conductive layer 2 to 5 to 500 nm, preferably to 5 to200 nm.

Ultra fine carbon fiber such as carbon nanotube, carbon nanohorn, carbonnanowire, carbon nanofiber, and graphite fibril, ultra fine metal fibersuch as metal nanotube and metal nanowire made of platinum, gold,silver, nickel, and silicon, and ultra fine metal oxide fiber such asmetal oxide nanotube or metal oxide nanowire made of zinc oxide are usedfor the ultra fine conductive fiber 3 in the conductive layer 2. Thefiber with the diameter of 0.3 to 100 nm and the length of 0.1 to 20 μm,especially 0.1 to 10 μm is preferably used. Since the ultra fineconductive fibers 3 are dispersed, without being densely concentrated,so that each fiber or bundle of the fibers is separated from otherfibers or bundles, it is possible to acquire the article with the lighttransmission of above 50% when the surface resistivity of the conductivelayer 2 is 10⁰ to 10¹Ω/□ and, the light transmission of above 75%, whensurface resistivity is 10² to 10³Ω/□, and the light transmission ofabove 88% when the surface resistivity is 10⁴ to 10⁶Ω/□, and the lighttransmission of above 93% when the surface resistivity is 10⁷ to10¹¹Ω/□. The light transmission indicates the transmission rate of thelight with 550 nm wavelength measured by a spectrometer.

Carbon nanotube has a very small diameter of 0.3 to 80 μm among theultra fine conductive fibers 3. Since the carbon nanotubes or bundles ofthe tube are separated from other tubes or bundles, there are very fewobstacles for light transmission, achieving the transparent conductivelayer 2 with the light transmission of above 50%. The ultra fineconductive fibers 3 in the conductive layer 2 are in contact with eachother, and yet dispersed well, without being densely concentrated, sothat each fiber or bundle of the fiber is separated from other fibers orbundles, allowing the flow of electricity. Therefore, it is possible tocontrol the surface resistivity with the scope of 10⁰ to 10¹¹Ω/□, whenthe estimated content of the ultra fine conductive fiber 3 in theconductive layer 2 is 1.0 to 450 mg/m². The value of the estimatedcontent of the fiber can be obtained by following the steps describedbelow. First, observe the conductive layer 2 by an electron microscopy,measuring the area occupied with the ultra fine conductive fiber in theplan area. Then, measure the thickness of the conductive layer. Then,multiply the value of the fiber area by the thickness of the conductivelayer acquired from the electro microscopic observation and the specificgravity of ultra fine conductive fiber (value 2.2, the average of2.1-2.3, reported as the specific gravity of graphite is used when theultra fine conductive fiber is made of carbon nanotube).

Here, the expression ‘not densely concentrated’ denotes that there is nolump of fibers with the average diameter, which is the average of thelonger diameter and the shorter diameter, of above 0.5 μm when theconductive layer is observed by an optical microscopy.

The carbon nanotube described above includes multi-layered carbonnanotube, which has a plurality of tubes made of carbon walls withdifferent diameters enclosed around the shared center axis andsingle-layered carbon nanotube, which has a single enclosed carbon wallaround the center axis.

There is a plurality of tubes made of carbon walls with differentdiameters enclosed around the shared center axis in the multi-layeredcarbon nanotube. The carbon walls are configured as hexagonal stackingstructure. Some multi-layered carbon nanotube has a carbon wall spiralthat makes a plurality of layers. The desirable multi-layered carbonnanotube has 2 to 30 carbon wall layers. An excellent light transmissionis acquired when the multi-layered carbon nanotube described above isdispersed as described above in the conductive layer. The more desirablecarbon nanotube has 2 to 15 carbon wall layers. Usually, themulti-layered carbon nanotube is dispersed with each piece of the carbonnanotube separated from other pieces. However, in some cases, the 2 to 3layered carbon nanotubes form bundles, which are dispersed as describedabove.

The single-layered carbon nanotube has a single enclosed carbon wallaround the center axis. The carbon wall is configured as hexagonalstacking structure. The single-layered carbon nanotube is not easilydispersed piece by piece. Two or more tubes form a bundle. The bundlesare not densely concentrated or intensely intertwined with each other.The bundles are simply crossing each other, making contact with eachother, dispersed in or on the conductive layer. The preferable bundle ofthe single-layered carbon nanotube has 10 to 50 tubes.

The surface resistivity of 10⁰ to 10¹¹Ω/□ of the conductive article Pwith the conductive layer 2, where the ultra fine conductive fibers 3are loosely crossing each other, is obtained with the excellentconductivity and the anti-electrostatic property, because the ultra fineconductive fiber 3 are loosely crossing each other, allowing the enoughflow of electricity, even with the reduced thickness of 5 to 500 nm forthe conductive layer 2 when the estimated content of the ultra fineconductive fiber 3 in the conductive layer 2 is 1.0 to 450 mg/m². Sincethe ultra fine conductive fiber is separated from other fibers and thereis no lump, there are very few obstacles for light transmission,achieving the good transparency. The transparency is also improved,because the estimated content of the ultra fine conductive fiber 3 isreduced, as the thickness of the conductive layer 2 gets thinner.

The surface resistivity of 10⁴ to 10¹¹Ω/□ of the conductive layer 2 canbe obtained even if the estimated content of the ultra fine conductivefiber 3 is reduced to 1.0 to 30 mg/m². Also, the conductive layer 2 withthe excellent transparency (the light transmission of above 88%) isacquired. Therefore, the transparent article can be acquired whentransparent resin or glass is used for the substrate 1. The transparentconductive polycarbonate resin plate with the light transmission ofabove 78%, the haze of below 2%, and the anti-electrostatic property isobtained when the transparent polycarbonate resin with the thickness ofabout 3 mm is used as the substrate 1.

The surface resistivity of 10² to 10³Ω/□ of the conductive layer 2 isobtained when the estimated content of the ultra fine conductive fiber 3in the conductive layer 2 is increased to 30 to 250 mg/m². Also, thetransparent conductive layer 2 is acquired (the light transmission ofabove 75%). Therefore, the transparent article with the low resistivelycan be acquired when transparent resin or glass is used for thesubstrate 1. The transparent conductive polycarbonate resin plate withthe excellent conductive property, which has the light transmission ofabove 65% and the haze of below 4%, is obtained when the transparentpolycarbonate resin with the thickness of about 3 mm is used as thesubstrate 1. This resin plate also has the electromagnetic shieldproperty.

The surface resistivity of 10⁰ to 10¹Ω/□ of the conductive layer 2 isobtained when the estimated content of the ultra fine conductive fiber 3in the conductive layer 2 is increased to 250 to 450 mg/m², whilekeeping the transparency of the conductive layer 2 (the lighttransmission of above 50%). Therefore, the transparent conductivearticle can be acquired when transparent resin is used for the substrate1. The transparent conductive polycarbonate resin plate with theexcellent conductive property, which has the light transmission of above45% and the haze of below 5%, is obtained when the transparentpolycarbonate resin with the thickness of about 3 mm is used as thesubstrate 1. This resin plate also has the electromagnetic shieldproperty. The light transmission of the conductive layer 2 can beobtained by correcting the light transmission of the light with 550 nmwavelength of the article using the light transmission of the substrate.A spectrometer is used for measuring. The transmission and the haze aremeasured according to ASTM D 1003.

The improvement of the dispersion of the ultra fine conductive fiber 3is important to achieve the better conductivity and transparency of theconductive layer 2 by adding a large amount of the ultra fine conductivefiber 3 to the conductive layer 2. It is also important to form thethinner conductive layer 2 by reducing the viscosity of the coatingsolution. Therefore, the disperser should be used for the betterdispersion. Macromolecule disperser and coupling agent such asalkylammonate solution of acid polymer, tertiary amine modified alkylco-polymer, and co-polymer between polyoxyethyllene and polyoxypropyleneare used as the disperser. Additive such as ultra-violet ray absorbent,surface modifier, and stabilizer can be added to the conductive layer 2in order to achieve the durability against weathering and otherproperties.

The transparent thermo-plastic resin, especially polyvinylchloride,co-polymer between vinylchloride and vinyl acetate,polymethylmethacrylate, nitrocellulose, chlorinated polyethylene,chlorinated polypropylene, and fluorovinylidene and the transparenthardening resin that is hardened by the application of heat,ultra-violet ray, electric beam or radioactive ray, especially melamineacrylate, urethane acrylate, epoxy resin, polyimid resin, and siliconresin such as acryl-transformer silicate are used as a binder.Therefore, the conductive layer 2, which is made of the transparentbinder and the ultra fine conductive fiber, is a transparent layer.Also, inorganic material such as colloidal silica can be added to thebinder. When the substrate 1 is made of a transparent thermo-plasticresin, the same transparent thermo-plastic resin or the differenttransparent thermo-plastic resin with the mutual-solubility ispreferably used as the binder for acquiring the transparent conductivearticle. The article P with the durability against wearing can beobtained when the binder with a hardening resin or colloidal silica isused. Since the conductive layer 2 is formed on the surface of thesubstrate 1, adequate binder should be chosen to improve the particularproperty such as the durability against weathering, surface strength,and durability against wearing.

When the estimated content of the ultra fine conductive fiber 3 in theconductive layer 2 is 1.0-450 mg/m², and when the thickness of theconductive layer 2 is reduced to 5-500 nm, the surface resistivity of10⁰ to 10¹¹Ω/□ with the excellent conductivity, the anti-electrostaticproperty, and transparency is obtained, because the ultra fineconductive fibers 3 or the bundle of the fiber are dispersed so thateach fiber or bundle is separated from other fibers or bundles. Thepreferable estimated content of the ultra fine conductive fiber 3 is 1.0to 200 mg/m² and the preferable thickness of the conductive layer 2 is 5to 200 nm. The powdered conductive metal oxide of 30 to 50 weight % canbe added beside the ultra fine conductive fiber to the conductive layer2.

The conductive article P described above can be efficiently produced,for example, by the following methods. First, the binder for forming theconductive layer is solved into a volatile solvent. The ultra fineconductive fiber 3 is equally dispersed in this solution, making acoating solution, which is then applied to one surface of the substrate1. The conductive layer 2 is obtained by drying the coating solution onthe substrate 1, forming the conductive article P. In the second method,the coating solution is applied to the surface of the thermoplasticresin film, which is the same thermoplastic resin film as that thesubstrate 1 or the different thermo-plastic resin film with themutual-solubility. Then, the coating solution is dried on the conductivefilm, forming the conductive film with the conductive layer 2. Theconductive film is placed to one surface of the substrate 1 throughthermal pressing or roll pressing, forming the conductive article P. Inthe third method, the coating solution is applied to and dried on apeeling-off film made of polyethyleneterephtalate, forming theconductive layer 2. Then, if necessary, an adhesive layer is formed onthe conductive layer 2, forming a transfer film. The transfer film ispressed on one surface of the substrate 1, transferring the conductivelayer 2 or the both adhesive layer and the conductive layer 2. Theconductive article P is obtained. Also, the article of this inventioncan be produced by any conventional methods.

When the article P is formed through the first method, it is importantto apply the thermal pressing at the final stage of the forming, becausethe thermal pressing can shrink the conductive layer 2 in the verticaldirection. The frequency of contact between the ultra fine conductivefibers, which are dispersed in the conductive layer 2, increases and thespace between the fibers is reduced, promoting the better flow ofelectricity, when the conductive layer 2 is pressed down in the verticaldirection. This method has an effect to further reduce the surfaceresistivity. If the latter methods, the laminating method or transfermethod is employed, the thermal pressing at the final stage of theproduction is not necessarily required, because the conductive layer hasalready been pressed down during the thermal pressing or thetransferring process. Also, the final thermal pressing is not requiredif the desirable conductivity for the particular use of the conductivearticle has already been achieved before its application.

The following examples illustrate embodiments of the invention, butshould not be viewed as limiting the scope of the invention.

EXAMPLES Comparative Example 1 and Example 1

Powdered vinylchloride resin as the binder is solved into cyclohexanonused as a solvent. The multi-layered carbon nanotube (product ofTsinghua-Nafine Nano-Powder Commercialization Engineering Center, withthe average outer diameter of 10 nm) is added to the solution describedabove with the content percentage shown in the Table 1. Also,alkylammonate solution of acid polymer, of 10 weight % of themulti-layered carbon nanotube is added to and equally dispersed in thesolution as the disperser. Two kinds of coating solution with thedifferent content percentage of the multi-layered carbon nanotube andthe binder are acquired.

Vinylchloride resin film with the thickness of 0.1 mm is used as thesubstrate. The coating solution is applied to the surface of thesubstrate with the variety of thickness. Then, the substrate is placedon the vinylchloride resin sheet with the thickness of 0.5 mm after thesolution is dried and hardened. Then, the substrate is pressed intemperature of 160° C. with the pressure of 30 kg/cm². Six kinds oftransparent conductive vinylchloride resin sheets a-f, each of which hasthe conductive layer with the different content percentage of themulti-layered carbon nanotube and the different thickness, are acquired.Also, the vinylchloride resin sheet g for the comparative example 1 isprepared by pressing the vinylchloride resin film as the substrate andthe vinylchloride resin sheet together.

The light transmission, the haze and the surface resistivity aremeasured for each of the transparent conductive vinylchloride resinsheets a-f and for the vinylchloride resin sheet g for comparison. Theresults are listed in the Table 1. The estimated content of the carbonnanotube of each of the resin sheets and the light transmission of thelight with 550 nm wavelength of the conductive layer of each of thesheets are also listed in the Table 1.

The light transmission and the haze are measured by a direct readinghaze computer HGM-2DP, a product of Suga Shikenki according to ASTMD1003. The surface resistivity is measured by a Highlester produced byMitsubishi Kagaku, according to ASTM D 257 or measured by a Rollesterproduced by Mitsubishi Kagaku, according to ASTM D991. The lighttransmission is measured by a Shimazu auto-recording spectrometerUV-3100PC produced by Shimazu Seisakusho. The difference in the lighttransmission of the light with 550 nm wavelength between the transparentconductive vinylchloride resin sheets and the vinylchloride resin sheetfor comparison is recorded. Table 1

The content percentage of the multi-layered carbon nanotube and thethickness are different between the resin sheets c and e, or the resinsheets d and f. However, each pair shows about the same surfaceresistivity, because each pair has about the same estimated content ofthe multi-layered carbon nanotube, as seen from the Table 1. As to theresin sheets a, b, c, and d, as the content percentage of themulti-layered carbon nanotube increases from 3 mg/m² to 20 mg/m², thesurface resistivity decreases from 10⁷Ω/□ to 10⁴Ω/□, showing theimproving anti-electrostatic property, and the light transmissiondecreases from 88% to 80%, while keeping the good transparency of above80%. As it is obvious from this result, the surface resistivity and thelight transmission decrease in proportion to the increase of theestimated content of the multi-layered carbon nanotube, even though thecontent percentage of the multi-layered carbon nanotube and thethickness of the layer are different among the resin sheets, if thecarbon nanotube is dispersed without being densely concentrated.Therefore, the estimated content of the carbon nanotube should be 3 to20 mg/ m² in order to obtain the surface resistivity of 10⁴Ω/□ to10⁷Ω/□. If the lower surface resistivity is desired, the estimatedcontent of the multi-layered carbon nanotube should be furtherincreased. The estimated content of the multi-layered carbon nanotubecan be increased either by increasing the content percentage of thecarbon nanotube or increasing the thickness of the conductive layer.

There is no big difference in haze among the transparent conductivevinylchloride resin sheets a-f. The light transmission of the resinsheets a-f is lower than that of the light transmission of the resinsheet g of the comparative example, by 3 to 10%. But they have theenough light transmission of above 80% for the practical use of thetransparent resin sheet.

Example 2

The multi-layered carbon nanotube (product of Tsinghua-NafineNano-Powder Commercialization Engineering Center, with the average outerdiameter of 10 nm) and tertiary amine modified alkyl co-polymer as thedisperser are added to and equally dispersed in ethanol solvent. Thiscoating solution is prepared such that it has 0.007 weight % of themulti-layered carbon nanotube and the 0.155 weight % of the disperser.

This coating solution is applied to the surface of a polycarbonateplate, which is a product of Takiron Co. Ltd., with the thickness of 3mm, the light transmission of 90.2%, and the haze of 0.40%. Thetransparent conductive polycarbonate resin plate with the conductivelayer of the thickness of 29 nm and the estimated content of themulti-layered carbon nanotube of 2.5 mg/m² is obtained after thesolution is dried. The surface resistivity and the light transmission ofthe conductive layer of the resin plate are measured by the same way asthat of the example 1. The surface resistivity is 3.2×10¹⁰Ω/□, and thelight transmission is 95.0%. The light transmission and the haze of thetransparent conductive polycarbonate are measured by the same way asthat of the example 1. The light transmission is 83.8% and the haze is1.0%.

Example 3

1.7 weight % of the powdered vinylchloride resin as the binder is solvedinto cyclohexanon solvent. The single-layered carbon nanotube (productof Carbon Nano Technology, with the diameter of 0.7-2 nm) andalkylammonate solution of acid polymer, as a disperser are added to andequally dispersed in the solution. This coating solution has 0.3 weight% of single-layered carbon nanotube and 0.18 weight % of disperser. Thiscoating solution is applied to and dried on the surface of acryl filmwith the thickness of 100 μm, acquiring the conductive laminate film.The transparent conductive vinylchloride resin plate is obtained bypressing the laminate film described above to the vinylchloride resinplate with the thickness of 3 mm in the temperature of 160° C. with thepressure of 30 Kg/cm².

The conductive layer of this resin plate is observed by a transmissionelectron microscopy (a product of Nihon Denshi Kogyo Corp., JEM-2010),measuring the area ratio of the single-layered carbon nanotube. The arearatio of the single-layered carbon nanotube is 11.1%. The thiclcess ofthe conductive layer is 65 nm. Therefore, the estimated content of thesingle-layered carbon nanotube is 15.9 mg/m², acquired by multiplyingthe area ration 11.1% by the thickness of 65 nm and the specific gravity(2.2). The surface resistivity and the light transmission of theconductive layer of the resin plate are measured by the same manner asthat of the example 1. The surface resistivity is 3.3×10⁷Ω/□, and thelight transmission is 92.8%. The light transmission and the haze of thetransparent conductive vinylchloride resin plate are measured by thesame way as that of the example 1. The light transmission is 80.1% andthe haze is 1.6%.

Additionally, the conductive layer of the transparent conductivevinylchloride resin plate is observed by an optical microscopy (aproduct of Nikon Corp., OPTIPHOTO 2-POL). No lump with the size of 0.5μm is observed. Then, the conductive layer of the resin plate isobserved by a transmission electron microscopy. As it is seen from FIG.4, the single layered carbon nanotube is dispersed well, with no lumpwith the size of 0.5 μm. Although the single layered carbon nanotubesare somewhat bent, the bundles are equally dispersed so that each bundleis separated from other bundles, and yet in contact, simply crossingeach other.

Example 4

The coating solution is prepared by the following procedure.Single-layered Carbon nanotube (synthesized by referring to ChemicalPhysics Letters, 323 (2000) P 580-585, with the diameter of 1.3-1.8 nm)and the co-polymer between poly oxy-ethylene and poly oxy-propylene asthe disperser are added to and dispersed in the mixture of isopropylenealcohol and water (with the compound ratio of 3:1) as a solvent. Thiscoating solution is prepared such that it has 0.003 weight % ofsingle-layered carbon nanotube and 0.05 weight % of disperser. Thiscoating solution is applied to the surface of a polyethyleneterephtalatefilm with the thickness of 100 μm (with the light transmission of 94.5%,and the haze of 1.5%). After drying the solution, the film is coatedwith the urethane acrylate solution diluted to 1-600^(th) with methylisobutyl ketone, and then dried. The transparent conductivepolyethyleneterephtalate film is obtained.

The conductive layer of the film is observed by a scanning electronmicroscopy (a product of Hitachi Seisakusho, S-800). The area ratio ofthe single-layered carbon nanotube is 70.3%. The thick ness of theconductive layer is 47 nm. Therefore, the estimated content of thesingle-layered carbon nanotube in the conductive layer is 72.7 mg/m²,acquired by multiplying the area ratio of 70.3% by the thickness of 47nm and the specific gravity (2.2). The surface resistivity and the lighttransmission of the conductive layer of the film are measured by thesame method used in the example 1. The surface resistivity is 5.4×10²Ω/□and the light transmission is 90.5%. The light transmission and the hazeof the transparent conductive polyethyleneterephtalate film are measuredby the same way as that of the example 1. The light transmission is85.8% and the haze is 1.8%.

Additionally, the conductive layer of the transparent conductivepolyethyleneterephtalate film is observed by an optical microscopy. Nolump with the size of 0.5 μm is observed. Then, the conductive layer ofthe film is observed by a transmission electron microscopy. As it isseen from FIG. 5, the single-layered carbon nanotube is dispersed well,with no lump. The bundles of the single-layered carbon nanotube areequally dispersed so that each bundle is separated from other bundles,and yet in contact, simply crossing each other.

Example 5

The coating solution, which is used in the Example 4, is applied to anddried on the surface of a polyethyleneterephtalate film used in theExample 4, obtaining the transparent conductive polyethyleneterephtalatefilm with the estimated content of the carbon nanotube in the conductivelayer of 267.3 mg/m². The surface resistivity and the light transmissionof the conductive layer of the film are measured by the same method usedin the example 1. The surface resistivity is 8.6×10¹Ω/□ and the lighttransmission is 60.6%. The light transmission and the haze of thetransparent conductive polyethyleneterephtalate film are measured by thesame way as that of the example 1. The light transmission is 57.1% andthe haze is 5.4%.

Comparative Example 2

1.7 weight % of the powdered vinylchloride resin as the binder is solvedinto cyclohexanon solvent. The single-layered carbon nanotube used inthe Example 3 and aluminum-coupling agent as a coupling agent are addedto and equally dispersed in the solution. This coating solution has 0.3weight % of single-layered carbon nanotube and 0.12 weight % of couplingagent. This coating solution is applied to and dried on the surface ofacryl film, as in the Example 3, acquiring the conductive laminate film.The transparent vinylchloride resin plate is obtained by pressing thelaminate film described above to the surface of the vinylchloride resinplate.

The conductive layer of the film is observed by a transmission electronmicroscopy. The area ratio of the carbon nanotube is 12.0%. Thethickness of the conductive layer is 62 nm. Therefore, the estimatedcontent of the carbon nanotube in the conductive layer is 16.4 mg/m²,acquired by multiplying the area ration 12.0% by the thickness of 62 nmand the specific gravity (2.2). The surface resistivity and the lighttransmission of the conductive layer are measured by the same methodused in the example 1. The surface resistivity is 2.2×10¹⁰Ω/□ and thelight transmission is 92.5%. Although the estimated content of thecarbon nanotube and the light transmission are almost the same as thoseof the Example 3, the surface resistivity is higher by 10³Ω/□.

The conductive layer of the resin plate is observed by an opticalmicroscopy. As it is seen from FIG. 6, the carbon nanotube is notdispersed enough and there are pluralities of lumps. The lumps with thesize of 0.5 μm are observed. The biggest size of the lump reaches 10 μm.The large difference in the surface resistivity between the Example 3and the Comparative Example 2 is due to the presence of the lump of thecarbon nanotube. That is, the Example 3 has the excellent surfaceresistivity because there is no lump of the carbon nanotube. The carbonnanotubes or bundle of the tube are dispersed in the conductive layer oron the surface of the conductive layer so that each tube or bundle areseparated from other tubes or bundles, and yet simply crossing eachother in the Example 3. The loosely crossing carbon nanotubes arepresent in a broader area, increasing the frequency of contact betweenthe carbon nanotubes. As a result, the improved conductivity isacquired.

Other embodiments and uses of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. All references cited herein,including all publications, U.S. and foreign patents and patentapplications, are specifically and entirely incorporated by reference.It is intended that the specification and examples be consideredexemplary only with the true scope and spirit of the invention indicatedby the following claims. TABLE 1 resin sheet layer CNT total 550 nmlayer components (Wt %) thickness content registivity transmission hasetransmission No CNT disperser binder (nm) (mg/m²) (Ω/□) (%) (%) (%) a 202 78 11 3.2 1.21 × 10⁷ 87.8 1.0 97.2 b 20 2 78 21 6.5 1.73 × 10⁶ 86.40.9 96.0 c 20 2 78 32 9.8 2.89 × 10⁵ 85.2 0.9 — d 20 2 78 65 20.0 4.51 ×10⁴ 79.5 0.9 88.7 e 60 6 34 9 9.7 1.03 × 10⁵ 85.5 0.8 — f 60 6 34 1919.5 7.77 × 10⁴ 80.6 1.0 89.8 g — — — — — >10¹⁴ 90.8 1.3 —CNT: Multi-wall carbon nanotubes

1. A conductive article comprising: a substrate; and a transparent andconductive layer comprising fine conductive fibers and formed on atleast one face of the substrate, wherein the fibers are electrically incontact with each other and dispersed so as not to form agglomerates ofsaid fibers.
 2. The conductive article of claim 1, wherein the fibersare electrically in contact with each other and dispersed so that eachof the fibers is separated from other fibers, or that each of bundles ofthe fibers is separated from other bundles.
 3. The conductive article ofclaim 1, wherein the fibers are carbon fibers.
 4. The conductive articleof claim 1, wherein carbon fibers are carbon nanotubes.
 5. Theconductive article of claim 1, wherein the fibers are multi-wall carbonnanotubes, and each of the carbon nanotubes is separated from othercarbon nanotubes while maintaining electrical contact between thenanotubes.
 6. The conductive article of claim 1, wherein the fibers aresingle-wall carbon nanotubes that form bundles of the carbon nanotubes,and each of the bundles is separated from other bundles whilemaintaining electrical contact between the bundles.
 7. The conductivearticle of claim 1, wherein the fibers are double-wall or triple-wallcarbon nanotubes that form bundles of the carbon nanotubes, and each ofthe bundles is separated from other bundles while maintaining electricalcontact between the bundles.
 8. The conductive article of claim 1,wherein the conductive article has a surface resistivity of from 10⁰ to10¹¹

/□.
 9. The conductive article of claim 1, wherein the transparent andconductive layer has a surface resistivity of from 10⁰ to 10¹

/□ and a 550 nm light transmittance of at least 50%.
 10. The conductivearticle of claim 1, wherein the transparent and conductive layer has asurface resistivity of from 10² to 10³

/□ and a 550 nm light transmittance of at least 75%.
 11. The conductivearticle of claim 1, wherein the transparent and conductive layer has asurface resistivity of from 10⁴ to 10⁶

/□ and a 550 nm light transmittance of at least 90%.
 12. The conductivearticle of claim 1, wherein the transparent and conductive layer has asurface resistivity of from 10⁷ to 10¹¹

/□ and a 550 nm light transmittance of at least 93%.
 13. The conductivearticle of claim 1, wherein the substrate is formed of a transparentsynthetic resin.
 14. A conductive article comprising: a substrate madeof a thermoplastic resin; and a transparent and conductive layercomprising carbon nanotubes and formed on at least one face of thesubstrate, wherein the carbon nanotubes are electrically in contact witheach other and dispersed so that each of the carbon nanotubes isseparated form other carbon nanotubes, or that each of bundles of thecarbon nanotubes is separated from other bundles.
 15. A method formanufacture of a conductive article comprising: applying a layer of fineconductive fibers to a surface of a substrate, wherein the fibers areelectrically in contact with each other and dispersed so as not to formagglomerates of said fibers.
 16. The method of claim 15, wherein thefine conductive fibers are carbon nanotubes.
 17. The method of claim 15,wherein the conductive article has a surface resistivity of from 10⁰ to10¹¹

/□.
 18. The method of claim 15, wherein the conductive article has asurface resistivity of from 10⁰ to 10¹

/□ and a 550 nm light transmittance of at least 50%.
 19. The method ofclaim 15, wherein the conductive article has a surface resistivity offrom 10² to 10³

/□ and a 550 nm light transmittance of at least 75%.
 20. The method ofclaim 15, wherein the conductive article has a surface resistivity offrom 10⁴ to 10⁶

/□ and a 550 nm light transmittance of at least 90%.
 21. The method ofclaim 15, wherein the substrate is formed of a transparent syntheticresin.